Recently, a MIMO technique using multiple transmit and receive (TX/RX) antennas is attracting much attention as one of techniques to satisfy an increasing demand for high-speed and high-quality data transmission. Since the MIMO technique performs communication using multiple channels of multiple antennas, it can greatly increase the channel capacity in comparison with the case of using a single antenna. For example, if a transmitter and a receiver use M number of TX antennas and M number of RX antennas, the channels of the antennas are independent of one another, and the bandwidth and the total TX power are fixed, the average channel capacity increases M times in comparison with the case of using a single antenna.
A Vertical-Bell Labs Layered Space Time (V-BLAST) system is one of systems that are designed to transmit/receive different independent signals through multiple antennas in a MIMO wireless communication system. A Maximum Likelihood (ML) detection scheme is an example of a scheme that provides the optimal RX performance when different signals are transmitted through multiple antennas as in the V-BLAST system. However, since the computational complexity of the ML detection scheme increases exponentially with an increase in the modulation order and the number of TX antennas, the ML detection scheme is very difficult to implement in practice.
A QR Decomposition-M (QRD-M) detection scheme is one of schemes that have relatively low complexity while having a similar performance to the ML detection scheme. The QRD-M detection scheme uses the R matrix characteristics of a QR-decomposed channel matrix to arrange signals in a tree structure as illustrated in FIG. 1, and selects M number of candidates at each stage to detect a TX signal. In the tree structure, the number of stages is equal to the number of TX antennas and each candidate has as many sub candidates as the modulation order.
A receiver using the QRD-M detection scheme selects M number of candidates with the smallest cumulative metric at each stage, and expands as many as candidates as the modulation order at the next stage with regard to only the previously selected candidates. The receiver repeats this process until the last stage to detect the final signals of the respective antennas. Herein, if the value M is equal to the modulation order, the receiver searches all the paths in the tree, which is equivalent to the use of the ML detection scheme. Thus, the detection performance of the QRD-M detection scheme depends on the value M. In order for the QRD-M detection scheme to approach the ML detection scheme in performance, the receiver must set the value M close to the modulation order. However, the computational complexity of the QRD-M detection scheme increases with an increase in the value M, which causes difficulty in implementation. There is therefore a need in the art for techniques to provide a modified QRD-M detection scheme that has low computational complexity while having a similar performance to the ML detection scheme.